A wide variety of memory devices can be used to maintain and store data and instructions for various computers and similar systems. In particular, nonvolatile memory such as, for example, flash memory is a type of electronic memory media that can maintain and store data content without consumption of power. Flash memory has become popular, at least in part, because it combines the advantages of the high density and low cost of erasable programmable read only memory (EPROM) with the electrical erasability of electronically erasable programmable read only memory (EEPROM). It is used in many portable electronic products, such as cell phones, smart cards, security cards, portable computers, voice recorders, thumbnail drives etc. The fact that flash memory can be rewritten as well as its retention of data without a power source, small size and light weight have all combined to make flash memory devices useful and popular means for transporting and maintaining data.
As flash memory devices have continued to evolve, the density of data stored in such devices has increased. Some technologies have been introduced and have evolved to improve the density of these flash devices such as, for example, Multi-Level Cell (MLC) based flash devices and MirrorBit based flash devices. Further, as memory devices increase in density, ensuring that data is effectively erased from a memory device to maintain data integrity, for example, during subsequent programming of the memory device is desirable.
Traditionally, flash memory devices have used band-to-band hot-hole (HH) injection to lower the Vt of the core cells during erase operations. During a HH injection erase operation a charge of approximately 6 volts is applied to bit lines (BLs) of a memory array. At the end of the HH injection erase, the BLs are typically discharged by the y-decoding circuitry of the memory array. The y-decoding circuits can reliably function when approximately 6 volts is discharged from the BLs. Another type of erase technique can be the Fowler-Nordheim Tunneling technique, which can also be known as a channel erase. During a channel erase, there can be a higher voltage level (e.g., approximately 10 volts) associated with the BLs, and such voltage is to be discharged after the erase is performed. Conventionally, there can be reliability and functionality issues, such as hot switching issues, within the y-decoding circuitry when a BL discharge is performed when the higher voltages associated with a channel erase are used.
It is desirable to discharge the higher BL voltages associated with a channel erase at a controlled rate to facilitate reliable operation of memory devices. Further, by controlling the discharge rate of associated BLs during a channel erase operation can help prevent disturbing the core cells of memory devices. A controlled BL voltage discharge rate can also avoid reliability and functionality issues for conventional discharge mechanisms associated with the y-decoder component during the discharge phase of channel erase operations.